to a more detailed account of the actual
work. Minesweeping may be divided into eight well-defined sections, as
follows:--

(1) _Fleet Sweeping._--Keeping clear the sea
routes of the battle fleet.

(2) _Exploratory Sweeping._--Searching the sea for
isolated groups or fields.

(3) _Routine Sweeping._--The daily or weekly
sweeping of areas, channels and coastal trade
routes, largely used by shipping.

(4) _Clearing Large Mine-fields._--Big
concentrations of ships to rapidly clear
important routes temporarily blocked by large
mine-fields.

(5) _Special Shallow-Water Sweeping._--Such as
that carried out off the Belgian coast by
specially constructed shallow-draught ships,
frequently with single-ship sweeps.

(6) _Convoy Sweeping._--Precautionary sweeping in
front of incoming and outgoing convoys. This was
regularly done even if the fair-way was covered by
routine sweeping.

(7) _Harbour Sweeping._--Precautionary sweeping
usually carried out by small craft at big naval
bases such as Portsmouth (Spithead) and Rosyth
(Firth of Forth) inside the submerged defences.

(8) _Searching at Low Tide._--This was done by
shallow-draught vessels of the M.L. type in order
to locate badly laid mines which might project
above the surface at low water. Several hundred
were discovered in this way.

In order to carry out these duties efficiently the heterogeneous fleet
of minesweepers was divided into small fleets stationed at the numerous
anti-submarine bases, and these were again subdivided into units of
ships especially adapted for the different classes of work. Each _pair_
of vessels had to be more or less alike in size, draught, speed and
manoeuvring ability to enable them to work efficiently in dual
harness. Consequently there were complete units of vessels specially
constructed for dealing rapidly with discovered mine-fields and for use
with the battle fleets. Shallow-draught vessels of the motor launch type
for work in the shallow water off the Belgian coast. Converted pleasure
steamers of the usual Thames, Mersey and Clyde type for convoy sweeping.
Motor launches for clearing fair-ways and for searchin